The switching power supply is a kind of power supply of utilizing the modern power electronic technology to control the on and off time ratio of the switching transistor to maintain the steady output voltage. Generally, the Pulse Width Modulation (PWM) is employed in the switching power supply, and the output voltage is maintained to be steady with the loop compensation for reducing the generation of the ripple.
In the switching power supply in prior art, the loop compensation circuit is commonly set to perform a fixed compensation to the output voltage. However in practical application, the input voltage and the loading often change from time to time, thus the output voltage also varies from time to time. If the fixed compensation is utilized, and the compensation speed and the variation rate of the output voltage are not consistent, not only the generation of the ripple cannot be reduced but it also results in that the output voltage has spiked and intensifies the unsteadiness of the output voltage.